The present invention pertains to processing of charge-based signals, such as are output from a charge coupled device (CCD). In particular, the present invention provides gain control and/or offset correction for such charge-based signals.
The output of a charge coupled device (CCD) is a series of charge packets. A CCD converts a detected signal into a series of charge packets, each of which is a charge based representation of the detected signal's magnitude at a particular point in time. To facilitate further processing of such a charge based signal, certain adjustments to its magnitude may be necessary or desirable.
One adjustment may be to adjust the gain of the signal so that the signal's magnitude remains within the optimum performance range of the signal processing circuitry. Another adjustment may be to compensate for a constant offset in the signal.
Conventional methods of gain control use amplifiers with feedback, and require voltage or current representations of the input signal. In certain circumstances, in particular in very cold environments such as 10.degree. Kelvin, the use of voltage or current amplifiers would produce excessive power dissipation. Current methods of offset control use amplifiers with clipping, and also require voltage or current representations of the input signals.
When the input signal is charge based, the conventional methods tend to be less desirable because conversion between charge and voltage representation of the signal may introduce excessive conversion error into the signal.
Therefore, it would be desirable to have a method of gain control and a method of offset control or correction that uses only the CCD technology charge packets.